Such a motor-vehicle door latch is described, for example, in DE 196 43 947 A1. Here, a so-called Hall-effect sensor chip is used, i.e. an electronic unit that can provide different current levels at its output and does so specifically depending on the proximity of an associated magnet. Such Hall-effect sensor chips are frequently used if, for example, the position of a latch fork in a motor-vehicle door latch is to be determined. In fact, such a motor-vehicle door latch is comprised of the two essential components, the door latch and the respective door bolt.
To the extent the door bolt engages a locking mechanism consisting of the latch fork and retaining pawl in the motor-vehicle door latch during closing of the respective motor-vehicle door, the latch fork is displaced: It first attains a prelocking position and then goes into the final locked position. The respective positions can be determined with the aid of the Hall-effect sensor chip or several such Hall-effect sensor chips and unambiguously detected by the controller. This is successful due to the association of the different current levels at the output of the sensor and/or Hall-effect sensor chip with the respective positions of the latch fork that are to be determined in the particular case.
Hall-effect sensor chips of this kind have certain disadvantages. They have a transient response which is due to the fact that the supply voltage of the Hall-effect sensor chip is normally pulsed. Due to the transient response behavior, the current signal emitted by the sensor and/or Hall-effect sensor can only be reliably analyzed by the controller with a delay. In light of the quick reaction times required today, this is a disadvantage. In addition, the Hall-effect sensor chips are relatively expensive and can malfunction. Malfunctions are due to the fact that the magnetic flow density of the respective magnet decreases because of external influences, age, mechanical damage, etc., and consequently, the at least two switch positions that are to be registered are no longer correctly present, or cannot be distinguished from one another.
Various methods are known in the prior art and from other contexts to the effect of working with switches and resistors in a latch (compare GB 2 309 481). Beyond that, it is known from JP 2001049952 to use a drive controller for a motor for opening and closing a motor-vehicle door with switches and resistors. But convincing suggestions for solving the above-cited problems are not seen here.